Various downhole operations are performed during the drilling and completion of a subterranean well, and also during the production of fluids from subterranean formations via the completed well. Representative downhole operations include perforating well casings, installing well devices, controlling well devices, and monitoring well parameters and output. Although downhole operations are performed at some depth within the well, they are typically controlled at the surface. For example, signal transmission conduits, such as electric cables and hydraulic lines, can be used to transfer signals from a depth within the well to a control system at the surface. Components of the control system then process the signals for controlling the downhole operations.
A recently developed method for controlling downhole operations employs devices within the well, which are configured to transmit and receive electromagnetic signals, such as radio frequency (RF) signals. These signals can then be used to control a tool or other device in the well, without the need to transmit and process the signals at the surface.
U.S. Pat. No. 6,333,691 B1 to Zierolf, entitled “Method And Apparatus For Determining Position In A Pipe”, and U.S. Pat. No. 6,536,524 B1 to Snider, entitled “Method And System For Performing A Casing Conveyed Perforating Process And Other Operations In Wells”, disclose representative systems which use electromagnetic transmitting and receiving devices. These devices are sometimes referred to as radio frequency identification devices (RFID). Typically, systems employing radio frequency devices require the radio frequency signals to be transmitted from the inside to the outside of the metal tubulars used in the well. In the past this has required penetrating structures such as sealed openings or windows in the metal tubulars. In general, these penetrating structures are expensive to make, and compromise the structural integrity of the tubulars.
Referring to FIGS. 1A and 1B, one such prior art system 10 for performing a perforating process in a well 12 using radio frequency signals is illustrated. The well 12 includes a well bore 16, and a well casing 14 within the well bore 16 surrounded by concrete 18. The well 12 extends from an earthen surface (not shown) through geological formations within the earth, which are represented as Zones A, B and C. The well casing 14 comprises a plurality of metal tubulars 20, such as lengths of metal pipe or tubing, attached to one another by collars 22 to form a fluid tight conduit for transmitting fluids.
The system 10 also includes a reader device assembly 24 on the well casing 14; a perforating tool assembly 26 on the well casing 14; a flapper valve assembly 28 on the well casing 14; and an identification device 30 (FIG. 1B) configured for movement through the well casing 14. The reader device assembly 24 includes a reader device collar 32 attached to the well casing 14, and a reader device 34 configured to transmit RF transmission signals at a selected frequency to the identification device 30, and to receive RF response signals from the identification device 30. The reader device 34 also includes a control circuit 38 configured to control the operation of the perforating tool assembly 26 and the flapper valve assembly 28 responsive to signals from the identification device 30.
In this system 10, the reader device collar 32 includes an electrically non-conductive window 36, such as a plastic or a composite material, that allows the RF signals to be freely transmitted between the reader device 34 and the identification device 30. One problem associated with the window 36 is that the strength of the well casing 14 is compromised, as a relatively large opening must be formed in the casing 14 for the window 36. In addition, the window 36 requires a fluid tight seal, which can rupture due to handling, fluid pressures or corrosive agents in the well 12. Further, the collar 32 for the window 36 is expensive to manufacture, and expensive to install on the casing 14.
Another approach to transmitting electromagnetic signals in a metal tubular is to place an antenna for an outside mounted reader device on the inside of the tubular, and then run wires from the antenna to the outside of the tubular. This approach also requires openings and a sealing mechanism for the wires, which can again compromise the structural strength and fluid tight integrity of the tubular.
It would be advantageous to be able to transmit electromagnetic signals between the inside and the outside of a metal tubular without compromising the strength of the tubular, and without penetrating and sealing the tubular. The present invention is directed to a method and a system for transmitting signals through metal tubulars without penetrating and sealing structures. In addition, the present invention is directed to systems for performing and monitoring operations in wells that incorporate metal tubulars. Further, the present invention is directed to a method for improving production in oil and gas wells using the system and the method.